1. Field of the Invention
The present invention relates to a control device for a battery.
2. Description of the Related Art
In the prior art, with a hybrid vehicle (HEV: hybrid electric vehicle) in which both an internal combustion engine and an electric motor are used together, or with an electric automobile (PEV: plug-in electric vehicle) that travels using only an electric motor, a battery assembly is used as the power supply for the electric motor, in which a plurality of battery modules, such as for example secondary lithium ion batteries or the like, are connected in series and series-parallel. Consideration is given by a charge/discharge control device for these secondary lithium ion batteries to the amount of charge of each of the battery cells (SOC: State Of Charge), to its temperature, to its internal resistance, and so on; and a current value or a power value is calculated within a permissible range such that none of the battery cells is subjected to excessive charge state or an excessive discharge state, and this value is notified to a motor controller that drives the electric motor.
Now, the internal resistance of each of these secondary lithium ion batteries changes drastically according to its temperature, and its internal resistance at low temperature is several times as great as at high temperature. The value of the internal resistance also changes according to differences in SOC, and has a tendency to be larger, the lower is the SOC. Moreover since, when a high current is discharged from the battery, the battery itself generates heat and thus its internal resistance changes, accordingly the internal resistance also varies according to the flow of discharge current, and this effect is particularly notable at low temperature.
Due to this, a technique has been disclosed in which the temperature dependence of the internal resistance of the battery is corrected using a temperature characteristic function that includes one or more exponential terms, and the states of deterioration of the secondary batteries are determined by estimating their internal resistances at a predetermined reference temperature (for example, refer to Japanese Laid-Open Patent Publication 2007-108063).